First off, cast aluminum isn't all that soft, it's more brittle than say 3003 or 5052. Second, you want to think of blue loctite as a quick setting removable cement. The good thing about it is that it seals the threads and actually acts as a lubricant when broken free. I've been using it for years on SS screws without issue. SS needs something to act as a lubricant for sure. I've locked up SS nuts on SS bolts when getting lazy about applying some sort of thread stuff.